Start with elastic and straightforward seams

Sewing undergarments at home is easier than you might think if you start with styles that use elastic and straight seams. The simplest projects—boxer briefs, boy shorts, and basic bras without underwire—require only a sewing machine, thread, elastic, and fabric. You do not need special skills; you need a pattern, the right measurements, and patience with fitting the elastic so it sits flat without rolling or bunching.

Most home sewers begin with boxer briefs or boy shorts because they use the same basic construction: two fabric pieces sewn together at the sides and crotch, then elastic threaded through a casing at the waist and leg openings. A bra without underwire is slightly more complex because you must attach cups to a band and sew straps, but the principle is the same—fabric pieces joined with seams, then elastic or binding added to finish the edges.

Key Takeaways

  • Boxer briefs and boy shorts are the easiest starting projects because they use only straight seams and elastic casings, with no underwire or complex shaping.
  • You will need a pattern sized to your actual measurements, not your clothing size, because undergarments fit closer to the body than regular clothes.
  • Elastic must be sewn into a casing (a tunnel of fabric) or attached flat to the edge with a zigzag stitch to prevent rolling and bunching.
  • Seams in undergarments should be finished with a zigzag stitch or serger to prevent fraying and reduce bulk against your skin.
  • Trying on your garment before closing the final seam lets you adjust fit without having to rip and resew.

Take your measurements correctly

Undergarments fit much closer to the body than regular clothes, so your measurements must be exact. Measure yourself wearing only a bra (or no bra if you prefer), standing in front of a mirror with the tape measure snug but not tight. Measure your bust at the fullest point, your waist at the narrowest point, and your hips at the fullest point. For boxer briefs or boy shorts, also measure your inseam—the distance from your crotch to your knee or wherever you want the leg to end.

Write down each measurement and compare it to the pattern's size chart before you buy the pattern. Patterns for undergarments often run smaller than patterns for regular clothes because they assume a closer fit. If your bust is 36 inches, you may need a size medium in a dress pattern but a size large in an undergarment pattern. Many pattern companies include a finished measurement chart that shows how much ease (extra room) is built in; for undergarments, ease is usually 0 to 2 inches, compared to 2 to 4 inches for a regular shirt.

Choose fabric that moves with your body

Undergarment fabric must stretch and recover—it should bounce back to its original shape after you pull it. Cotton jersey, nylon spandex blends, and power mesh are the most common choices. Cotton jersey is soft and breathable but less stretchy; nylon spandex blends (often called lycra blends) stretch more and dry faster; power mesh is firm and supportive. For your first project, cotton jersey or a nylon blend is easier to work with than power mesh because they do not slip as much under the presser foot.

Buy fabric from a store or online supplier that specializes in stretch fabrics or swimwear fabrics, not a general quilting store. The staff can tell you the stretch percentage—how much the fabric stretches in each direction—and recommend a needle and thread weight for your machine. Most undergarment projects need 1 to 2 yards of fabric depending on the style. Prewash your fabric in warm water and dry it on low heat before cutting, because stretch fabrics can shrink.

Sew seams with a stretch stitch or narrow zigzag

A regular straight stitch will break when you move in undergarments because the seam cannot stretch with the fabric. Instead, use a stretch stitch (a setting on most modern machines that looks like a broken line) or a narrow zigzag stitch set to a width of 1.5 to 2 millimeters and a length of 2 to 2.5 millimeters. Test your stitch on a scrap of your fabric first. The seam should stretch when you pull it without the thread breaking.

Sew all seams with a 5/8-inch seam allowance unless your pattern says otherwise. After sewing each seam, finish the raw edges with a zigzag stitch or a serger to prevent fraying and reduce bulk. If you do not have a serger, a three-step zigzag stitch (a setting on many machines) works well. Trim the raw edges close to the zigzag stitching with sharp scissors or pinking shears. This step takes extra time but keeps seams from itching against your skin.

Attach elastic without rolling or bunching

Elastic can be sewn into a casing (a tunnel of fabric you create by folding the edge over) or attached flat to the edge with a zigzag stitch. A casing is easier for beginners because the elastic is hidden and protected. To make a casing, fold the edge of the fabric to the inside by the width of your elastic plus 1/4 inch, press it flat with an iron, and sew close to the fold with a stretch stitch. Leave a 1-inch opening to insert the elastic.

Thread the elastic through the casing using a safety pin or bodkin (a small tool made for this purpose). Pin the elastic ends together, try on the garment, and adjust the elastic tension until it feels snug but not tight—you should be able to fit one finger under it comfortably. Sew the elastic ends together with a zigzag stitch, then sew the opening closed. For leg openings, use narrower elastic (usually 1/2 to 3/4 inch wide) than for the waist (usually 1 to 1.5 inches wide).

Try on and adjust before closing seams

Before you sew the final seams—usually the crotch seam and the side seams—try on your garment inside out. This is the moment to check that the leg openings are not too tight, the waist sits where you want it, and the crotch depth is correct. If the leg opening is too tight, you can add a wider elastic or remove some elastic tension. If the crotch is too deep or too shallow, you can adjust the seam line before you sew it permanently.

Mark any changes with a fabric pen or tailor's chalk, take off the garment, and sew the final seams. Once you close the crotch seam, you cannot easily adjust the fit without ripping and resewing. This step saves hours of frustration later.

Finish the edges and care for your finished garment

After all seams are sewn and elastic is attached, trim any loose threads and press the garment with a warm iron (not hot, which can damage stretch fabrics). If you have a serger, run the seams through it one more time to create a professional finish. If not, your zigzag-finished seams are complete.

Wash your finished undergarments in cool water with mild detergent and lay them flat to dry or hang them to dry. Do not use fabric softener, which breaks down elastic over time. Stretch fabrics last longer when they are not dried in a hot dryer; air drying keeps the elastic from degrading. Your first pair may not be perfect, but each project teaches you something about fit and construction that makes the next pair better.

Frequently Asked Questions

What needle should I use for stretch fabric?

Use a ballpoint or stretch needle (size 75/11 or 90/14) designed to slide between fibers rather than pierce them. A regular needle can skip stitches or break the fabric. Ask the staff at your fabric store which needle works best with your specific fabric blend.

Can I use regular thread for undergarments?

Regular polyester thread works, but thread made for stretch fabrics is slightly more flexible and less likely to break when the garment moves. The difference is small for beginners, so regular thread is fine for your first project.

How do I prevent the elastic from rolling?

Sew the elastic into a casing rather than attaching it flat to the edge. A casing keeps the elastic from rolling because it is enclosed on three sides. If you attach elastic flat, use a wide elastic (at least 1 inch) and sew it with a zigzag stitch on both long edges to anchor it.

What if my seams keep skipping stitches?

Skipped stitches usually mean your needle is dull, the wrong size, or the wrong type for your fabric. Replace the needle with a fresh ballpoint or stretch needle, and make sure you are using the correct needle size for your fabric weight. Also check that your thread is wound correctly and not tangled in the bobbin.

Can I use a pattern from a regular clothing website?

Patterns designed for regular clothes often do not account for the stretch and recovery of undergarment fabrics, so fit may be unpredictable. Use patterns from companies that specialize in swimwear or undergarments, such as Jalie, Simplicity (their stretch pattern line), or independent designers who sell on Etsy. These patterns are drafted with stretch fabric in mind.